1. Field of the Invention
The present invention relates to a method for preparing modified stannic oxide-zirconium oxide colloidal particles having a particle diameter of 4.5-60 nm which is formed by coating stannic oxide-zirconium oxide complex colloidal particles prepared by use of stannic oxide colloidal particles having a particle diameter of 4-50 nm obtained by reacting hydrogen peroxide solution and metal tin in an organic acid aqueous solution, preferably oxalic acid aqueous solution in such a manner that H2O2/Sn molar ratio is maintained at 2-10, preferably 2-4 and the concentration of tin oxides is 40% by weight or less with tungsten oxide-stannic oxide-silicon dioxide complex colloidal particles having a particle diameter of 2-7 nm.
The sol according to the present invention is used as a component of hard coating agent applied on a plastic lens surface and also for other various applications.
2. Description of the Related Art
A variety of metal oxide sols are already known.
There have been used sols of metal oxides having a high refractive index as a component of a hard coating agent applied on a plastic lens surface which is recently used much in order to improve the surface.
For example, a hard coating agent containing particles of metal oxides such as Al, Ti, Zr, Sn and Sb, etc. having a size of 1-300 nm is described in Japanese Patent Publication No. Sho 63-37142.
Although a stable sol of tungsten oxide alone is not known yet, Japanese Patent Laid-Open No. Sho 54-52686 proposes a sol obtained by addition of silicate in which a WO3:SiO2:M2O molar ratio (wherein, M represents alkali metal atom or ammonium group) is 4-15:2-5:1.
A silicate-stannate complex sol in which a molar ratio of Si:Sn is 2-1000:1 has been proposed in Japanese Patent Publication No. Sho 50-40119.
Japanese Patent Application Laid-Open No. Hei 3-217230 proposes a stable sol comprising a modified metal oxide colloid having a particle diameter of 4.5-60 nm and which is formed by coating colloidal particulate surfaces of metal oxide having a particle diameter of 4-50 nm and a valence of 3, 4 or 5 as nuclei with colloidal particles of a tungsten oxide-stannic oxide complex having a WO3/SnO2 weight ratio of 0.5-100 and a particle diameter of 2-7 nm, wherein the stable sol contains total metal oxides in an amount of 2-50% by weight.
Japanese Patent Laid-Open No. Hei 6-24746 proposes a stable sol of a modified SnO2—ZrO2 complex which comprises particles formed by coating surfaces of colloidal particle of metal oxide having a ZrO2/SnO2 weight ratio of 0.02-1.0 and a particle diameter of 4-50 nm as nuclei with colloidal particles of a WO3—SnO2 complex having a WO3/SnO2 weight ratio of 0.5-100 and a particle diameter of 2-7 nm.
In addition, Japanese Patent Laid-Open No. 2000-281344 discloses a stable sol which comprises modified stannic oxide-zirconium oxide complex colloidal particles having a particle diameter of 4.5-60 nm, wherein the particles are formed by coating surfaces of stannic oxide-zirconium oxide complex colloidal particles having a bonded structure of stannic oxide colloidal particles with zirconium oxide colloidal particles at a ZrO2/SnO2 ratio of 0.02-1.0 based on weights of these oxides and having a particle diameter of 4-50 nm as nuclei, with tungsten oxide-stannic oxide-silicon dioxide complex colloidal particles having a WO3/SnO2 weight ratio of 0.1-100, a SiO2/SnO2 weight ratio of 0.1-100 and a particle diameter of 2-7 nm, and wherein the sol contains total metal oxides in an amount of 2-50% by weight.
When these conventional metal oxide sols, particularly cationic metal oxide sols are used as a component of a hard coating agent, the stability of the obtained hard coating agent is insufficient and also transparency, adhesion, weather resistance, etc. of a hardened coating coated with the hard coating agent are insufficient. Further, if an Sb2O5 sol is used as a component of a hard coating agent, the Sb2O5 sol can no longer improve a refractive index of the hardened coating sufficiently when a refractive index of a plastic substrate in a lens is 1.6 or more, since a refractive index of Sb2O5 is about 1.65-1.70.
The silicate-stannate complex sol described in the above-mentioned Japanese Patent Publication No. Sho 50-40119 is obtained by decationizing a mixed aqueous solution of an alkali silicate and an alkali stannate, but an effect for improving a refractive index of a coating is also low in the case of use as a component of a hard coating agent as described above.
The sol of tungsten oxide described in the above-mentioned Japanese Patent Laid-Open No. Sho 54-52686 is obtained by adding a silicate to a tungstate aqueous solution which is obtained by decationizing a tungstate aqueous solution, but it is stable only at a strong acidic state and an effect for improving a refractive index of a coating is low in the case of use as a component of a hard coating agent.
The modified metal oxide sol described in the above-mentioned Japanese Patent Laid-Open No. Hei 3-217230 having a refractive index of 1.7 or more is stable, thus it can be used as a component of a hard coating agent for a plastic lens and it can satisfy almost all properties required for a hard coating such as damage resistance, transparency, adhesion, water resistance, weather resistance, etc. However, in case where a base material of lens has a refractive index of 1.7 or more, the refractive index of cured coating is no longer improved sufficiently.
The modified stannic oxide-zirconium oxide sol described in the above-mentioned Japanese Patent Laid-Open No. Hei 6-24746 having a refractive index of 1.7 or more is stable, thus it can be used as a component of a hard coating agent for a plastic lens, and it can satisfy almost all properties required for a hard coating such as damage resistance, transparency, adhesion, etc. However, in case where a base material of lens has a refractive index of 1.7 or more, it is desired that physical properties of the applied coating are further improved.
The modified stannic oxide-zirconium oxide sol described in the above-mentioned Japanese Patent Laid-Open No. 2000-281344 having a refractive index of 1.7 or more is stable, thus it can be used as a component of a hard coating agent for a plastic lens and it can overcome problems found when the conventional metal oxide sols are used, such as yellowing due to ultraviolet radiation, low water resistance, low moisture resistance and low weather resistance, and further it can satisfy almost all properties required for a hard coating such as damage resistance, transparency, adhesion, etc. However, in case where a base material of lens has a refractive index of 1.7 or more, it is desired that physical properties of the applied coating are further improved.